The present invention relates to a welded joint between a sheet-steel component and a light sheet metal component, in particular a sheet-aluminum component, by way of a lap or web weld with the aid of an additional part connected to the light sheet metal component at the rim and welded to the sheet-steel component.
An article "Resistance spot-welding of aluminum to steel" in the German periodical Schwei.beta.en und Schneiden 34, 1982, volume 1, pp 15-20 discusses an electrically resistance-welded joint between a steel sheet and a light metal sheet in which the two sheets overlap at the rim. Welding is carried out with the aid of a bimetallic composite material consisting of a roll-bonded intermediate sheet which, viewed along its wall thickness, consists of about 50% steel and about 50% aluminum. For welding, the two sheets are overlapped and the intermediate sheet manufactured from the composite material is arranged between them in the overlapping region. In this arrangement, the steel side of the intermediate sheet faces the steel sheet and the light-metal side faces the aluminum sheet. In this process, the sequence of operations is likewise complex since for each welding operation the intermediate sheet has to be inserted. This method of joining parts in a visible area is furthermore unfavorable since, due to the intermediate sheet, the overlap edge is very high and a large amount of effort is required to clean the overlap edge.
U.S. Pat. No. 2,566,871 shows a motor-vehicle door having a frame manufactured from aluminum and being clad with formed steel parts. As depicted in FIG. 9 of this patent, an additional part manufactured from steel is rivetted to the frame part. A steel bracket is welded to the other end of the additional part. For reasons of weight, motor vehicle manufacturers are increasingly producing large, and hence also heavy, cladding parts from light metal. However, the techniques described are unsuitable for aluminum covering panels which are arranged on a steel frame because it relates to the attachment of small steel parts to light-metal frame parts. During the production of the door, the additional part must furthermore be rivetted to the light-metal part in a defined position and the bracket welded on in a defined position. Due to the positionally accurate attachment of the additional part, this method of attachment is very time-consuming and costly.
German Patent 3,038,824 discloses the welding of a steel sheet to a light metal sheet arranged in abutting relationship, and an additional part is placed against the rear of the butt joint between the sheets. The additional part is manufactured from light metal and is clad with steel in the region of the steel sheet placed thereagainst. For welding, the additional part is placed with its clad region against the steel sheet and with the light-metal region against the light metal sheet and is then welded to the respective sheet by electric resistance welding. Since the two sheets are butt-welded, only a small amount of cleaning work is necessary on the visible side of the joint. It is advantageous that, with this joining method, it is also possible to dispense with other expensive joining devices such as rivets, screws etc. However, the sequence of work in the welding process is complex since for each weld an additional part must be inserted.
An object of the present invention is to further improve the welded joint such that a sheet-aluminum component and a sheet-steel component can be joined more simply in production.
That object has been achieved according to the present invention in that the additional part consists of an iron material and is lock-seamed to the rim of the light sheet metal component and the additional part is bonded to the light sheet metal component. By virtue of the positive-locking arrangement of the rim of the sheet-aluminum component in the seam of the additional part which is manufactured from iron material before fitting to and welding to the sheet-steel component, a sheet-aluminum component prepared in this way can be placed against and welded to the sheet-steel component in a simple manner.